The present invention relates to an organic electroluminescent device having an excellent light-emitting property such as high luminance efficiency.
An organic electroluminescent device (which will hereinafter be called xe2x80x9corganic EL devicexe2x80x9d) is a light-emitting device which makes use of the principle that when an electric field is applied, a fluorescent material emits light in response to the charge recombination of holes injected from an anode and electrons injected from a cathode. After C. W. Tang et al. of Eastman Kodak Company reported a low-voltage-driven organic EL device using a double layered structure (C. W. Tang, S. A. Vanslyke, Applied Physics Letters, Vol. 51, 913 (1987) and the like), studies on an organic EL device and materials have been briskly carried out. Tang et al. reported a multi-layered organic EL device using tris (8-hydroxyquinolinol aluminum) in a light-emitting layer and a triphenyldiamine derivative in a hole-transporting layer. This stacked structure gives such advantages as an improvement in the injection efficiency of holes into the light-emitting layer; blocking of electrons injected from a cathode; and confinement of the excitons into the light-emitting layer.
A double layered structure composed of a hole-injecting and transporting layer and an electron-transporting and light-emitting layer or a triple layered structure composed of a hole-injecting and transporting layer, a light-emitting layer and an electron-injecting and transporting layer is well known as an organic EL device. In order to increase the recombination efficiency of injected holes and electrons, various improvements in the device structure or fabrication process have been introduced to such multi-layered devices.
As a hole transporting material, triphenyl amine derivatives and aromatic diamine derivatives such as 4xe2x80x2,4xe2x80x2,4xe2x80x3-tris(3-methylphenylphenylamino)-triphenyl amine which is a star burst molecule and N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2-diamine are well known (for example, Patent Publications JP-A-8-20771, JP-A-8-40995, JP-A-8-40997, JP-A-8-53397, and JP-A-8-87122). As an electron transporting material, oxadiazole derivatives, triazole derivatives and the like are well known.
Chelate complexes such as tris(8-quinolinolate)aluminum complex, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives, oxadiazole derivatives and the like are known as light emitting materials. Since various color lights in a visible region from blue to red are obtained from these light emitting materials, there is increased expectation for industrialization of a full color organic EL device (refer to, e.g., JP-A-8-239655, JP-A-7-138561, and JP-A-3-200889).
Besides, various materials for the electroluminescent devices have been reported. However, in the case of some compounds, we can not use most method for film fabrication due to excessively strong intermolecular interactions. In addition, for such compounds having a strong intermolecular interaction, concentration quenching is observed when they are used as a light emitting material, which has decreased the luminance and luminous efficiency of the device.
Moreover, the materials used for the organic EL devices are required to have good charge transporting injecting properties. In recent days, organic EL devices with high brightness and long lifetime have been disclosed or reported, but any of them are not enough in these properties. It has been, therefore, desired to develop materials having a high performance.
In view of the above problems, an objective of this invention is to provide an organic EL device with an improved luminance luminous efficiencies and little limitation on to film fabrication method.
Another object of the present invention is to provide an organic electroluminescent device with improved luminance by using a compound having improved charge injecting properties.
The present inventors have repeated experiments to solve above problem, and found that an organic EL device having superior emission properties is obtained by using a compound having at least one substituted or unsubstituted cyclohexylidenemethine group. The compounds have the intermolecular interactions reduced by the steric hindrance of the cyclohexylidenemethine group. Thus, the concentration quenching is decreased when the compounds are used as a light emitting material, and the film comprising the compounds can be fabricated with ordinary method.
Some conventional compounds with aryl amine moety or styryl moety don""t have enough hole injection properties because their energy level of their highest occupied molecular orbital (HOMO) is too low. It has been known that some substituents shift the HOMO level slightly, but it is not enough to improve their hole injection properties. Then, there has been no method to shift the HOMO of such compounds to higher without effects on energy gap between HOMO and lowest unoccupied molecular orbital (LUMO), light emitting properties and carrier transpoting properties. The present inventors also found that the cyclohexylidenemethine group shifts the energy level of HOMO of the compounds to higher, which improves the hole injecting properties, without effect on the energy gap between HOMO and LUMO. Thus, the present invention was achieved.
An organic electroluminescent device according to the present invention comprises an anode, a cathode, and one or more organic thin film layers between the said anode and the said cathode, the organic thin film layer(s) including a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds having a cyclohexylidenemethine group, either singly or as a mixture.
The present inventors have found that an organic EL device using bis(diarylamino)arylene compound having a cyclohexylidenemethine group has improved light-emitting properties.
An organic electroluminescent device according to a first aspect of the present invention comprises an anode, a cathode, and one or more organic thin film layers placed between said anode and said cathode, the organic thin film layer(s) having a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds represented by the following general formula [A], either singly or as a mixture: 
wherein
Ar1 represents a substituted or unsubstituted aromatic hydrocarbon group having 5 to 42 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 4 to 42 carbon atoms;
each of Ar2 to Ar5 independently represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 6 to 20 carbon atoms;
each of X1 and X2 independently represents a divalent linking group; and
each of R1 to R20 independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted amino group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryloxy group, or a substituted or unsubstituted alkoxycarbonyl group, provided that two of R1 to R1 or R1 to R may form a ring and that Ar2 and Ar3 or Ar4 and Ar5 may be bonded to each other to form a ring.
In the general formula [A], it is preferable that at least one of the linking groups represented by X1 and X2 is a substituted or unsubstituted styryl group.
An organic electroluminescent device according to a second aspect of the present invention comprises an anode, a cathode, and one or more organic thin film layers placed between said anode and said cathode, the organic thin film layer(s) having a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds represented by the following general formula [B], either singly or as a mixture: 
wherein
Ar1 represents a substituted or unsubstituted aromatic hydrocarbon group having 5 to 42 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 4 to 42 carbon atoms;
each of Ar2 to Ar5 independently represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 6 to 20 carbon atoms;
each of R21 to R76 independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted amino group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryloxy group, or a substituted or unsubstituted alkoxycarbonyl group, two of R21 to R30, R31 to R40, R41 to R50, R51 to R60, and R61 to R76 may form a ring and Ar2 and Ar 3 or Ar 4 and Ar5 may be bonded to each other to form a ring.
The present inventors have found that an organic EL device using a compound having two 2,2-bis[4-(cyclohexylidenemethine)phenyl]vinyl groups linked to each other through a linking group has improved light-emittng properties. The diphenyl vinyl group improves the charge injection properties and cyclohexylidenemethine group gives improved charge injection properties. This significantly improves the luminous efficiency.
Therefore, an organic electroluminescent device according to a third aspect of the present invention comprises an anode, a cathode, and one or more organic thin film layers between said anode and said cathode, the organic thin film layer(s) having a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds represented by the following general formula [C]; either singly or as a mixture: 
wherein
each of R77 to R116 independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted amino group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryloxy group, or a substituted or unsubstituted alkoxycarbonyl group; any two of R77 to R86, R87 to R96, R97 to R106 and R107 to R116 may form a ring;
each of R117 to R132 independently represents a hydrogen atom, a halogen atom, a hydroxyl group, a substituted or unsubstituted amino group, nitro group, cyano group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted styryl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxycarbonyl group, or carboxyl group; any two of R117 to R132 may form a ring; and
X3 represents a divalent linking group.
An organic electroluminescent device according to a fourth aspect of the present invention comprises an anode, a cathode, and one or more organic thin film layers between said anode and said cathode, the organic thin film layer(s) having a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds represented by the following general formula [D]; either singly alone or as a mixture: 
wherein
each of Ar6 to Ar8 independently represents a substituted or unsubstituted aromatic hydrocarbon group having 5 to 42 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 4 to 42 carbon atoms; Ar6 to Ar8 may be bonded to each other to form a ring;
each of X4 and X6 independently represents a divalent linking group;
each of R133 to R162 independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted alkoxy group; any two of R133 to R142, R143 to R152 and R153 to R162 may form a ring;
l, m and n are each independently 0 or 1; and
l plus m plus n is an integer between 1 and 3, both inclusive.
An organic electroluminescent device according to a fifth aspect of the present invention comprises an anode, a cathode, and one or more organic thin film layers between said anode and said cathode, the organic thin film layer(s) having a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds represented by the following general formula [E]; either singly or as a mixture: 
wherein
each of Ar9 to Ar15 independently represents a substituted or unsubstituted aromatic hydrocarbon group having 5 to 42 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 4 to 42 carbon atoms; Ar10 and Ar11, Ar12 and Ar13, and Ar14 and Ar15 may be bonded to each other to form a ring;
each of X7 and X12 independently represents a divalent linking group;
each of R163 to R192 independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted alkoxy group; any two of R163 to R172, R173 to R182 and R183 to R192 may form a ring;
o, p and q are each independently 0 or 1; and
o plus p plus q is an integer between 1 and 3, both inclusive.
An organic electroluminescent device according to a sixth aspect of the present invention comprises an anode, a cathode, and one or more organic thin film layers placed between said anode and said cathode, the organic thin film layer(s) having a light-emitting layer, wherein at least one of the organic thin film layers contains one or more compounds represented by the following general formula [F]; either singly or as a mixture: 
wherein
each of Ar16 to Ar24 independently represents a substituted or unsubstituted aromatic hydrocarbon group having 5 to 42 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 4 to 42 carbon atoms, provided that Ar16 and Ar17, Ar18 and Ar19, Ar20 and Ar21, and Ar22 and Ar23 may be bonded to each other to form a ring;
each of X13 and X20 independently represents a divalent linking group;
each of R193 to R232 independently represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted alkoxy group, provided that two of R193 to R202, R203 to R212, R213 to R222 and R223 to R232 may form a ring;
r, s, t and u are each independently 0 or 1; and
r plus s plus t plus u is an integer between 1 and 4, both inclusive.
It has been found that the compounds represented by the compound represented by the general formulae [A] to [F] having a cyclohexylidenemethine group has a good carrier transporting property. It has been also found that an organic EL device prepared by using the compound as a hole- or electron-transporting material, or by using a mixture layer of the above material and another hole- or electron-transporting material, have a higher luminance than a conventional one. The organic electroluminescent device of the present invention thus contains these compounds alone or as a mixture as a light-emitting material and/or an electron transporting material and/or a hole transporting material. More specifically, an organic electroluminescent device according to the present invention may have an electron transporting layer, as one of the organic thin film layers, containing one or more compounds represented by the general formulae [A] to [F] having a cyclohexylidenemethine group. An organic electroluminescent device according to the present invention also may have a hole transporting layer, as one of the orbanic thin film layers, containing one or more compounds represented by the general formulae [A] to [F] having a cyclohexylidenemethine group.
The organic electroluminescent device of the present invention may contain the compound(s) represented by the general formula or the compound(s) having a cyclohexylidenemethine group at least on the terminal thereof in at least one organic thin film layer. The above-mentioned advantages are obtained particularly when the light-emitting layer is adjacent to the anode. An organic EL device of the present invention may have the light-emitting layer adjacent to the anode.
The present inventors have found that an organic EL device using anode which has been exposed to ultraviolet light at a wavelength of lower than 200 nm or oxygen plasma before fabrication of the organic thin film layer(s) in the case of the device having the light-emitting layer adjacent to the anode. Therefore, it is preferable to use such an anode when the light-emitting layer is adjacement to the anode.
It also has been found that an organic EL device with the organic thin film layer adjacent to the cathode containing a metal at the interface with the cathode has much better light emitting properties.